None.
The present invention relates generally to the manufacture of blow-molded thermoplastic products, and particularly concerns both a method and apparatus for accomplishing the separation of integrally formed gutter flash from a blow-molded product while the product is completely restrained by the product mold cavity of the apparatus.
It is common practice in the United States in connection with the manufacture of blow-molded thermoplastic resin products using conventional production blow-molding machines and known blow-mold assemblies to eject the molded product from the mold assembly with the simultaneously formed gutter flash integrally attached, and to afterwards completely separate the integrally attached flash from the ejected blow-molded product by subsequent combined operations such as sequential cutting and grinding or sequential shearing and grinding. The operating forces required to so-separate and remove such flash, either manually or by machine, sometimes are extremely large and often are beyond the available capacity of the blow-molding machine. The required flash separation and removal forces are especially substantial in cases where the blow-molding machine production cycle unit output is comprised of a single blow-molded product or multiple blow-molded products, each with integrally attached gutter flash, having either or both a substantial resin material wall thickness and a substantial total length of gutter flash trim edge.
In the teachings of U.S. Pat. No. 5,480,607 granted to Hobson a method of separating integrally attached flash from a product during the molding process is disclosed, but such method utilizes a step wherein the flash is temporarily secured to the apparatus blow-mold and the formed product is separated from the restrained integral flash by applying product mold ejector pin forces to the blow-molded product with the mold assembly in a partially open condition. The ejection forces required may be undesirably large and also generally cause ejector pin damage to the formed product in high-rate production cycles wherein the blow-molded product has an elevated temperature and a substantial degree of residual parison plasticity at time of flash separation and product ejection from its mold.
I have discovered a novel method of separating integrally attached gutter flash from a blow-molded product and also novel mold assembly constructions and a methods of assembly operation that may be used in conjunction with use of a conventional production blow-molding machine to achieve complete, or very nearly complete, separation of otherwise integrally attached gutter flash from blow-molded products both while the products are fully restrained by the mold apparatus and prior to product ejection from within the mold apparatus. Subsequently the individual blow-molded thermoplastic resin products and separated gutter flash are ejected from the mold assemblies in which they were formed and removed from the co-operating conventional production blow-molding machine. Because very short blow-molding machine operating cycle unit times may be achieved with the novel in-mold product de-flashing, and because the apparatus takes advantage of separate product and gutter flash removal procedures, the blow-molded thermoplastic resin products and separate gutter flash have no possibility of being inadvertently fused together.
Other objects and advantages of the present invention will become apparent during consideration of the detailed descriptions, drawings, and claims which follow.
The method of the present invention involves a basic step sequence of blow-molding an extruded and heated thermoplastic resin parison contained within co-operating blow-mold sub-assemblies to form a blow-molded product having integrally attached gutter flash, separating the integrally attached gutter flash from the blow-molded product while the molded product is fully restrained by the mold sub-assemblies and progressively along the product mold parting-line perimeter from one product dimensional limit to an opposite dimensional limit until gutter flash separation from the product is complete, and afterwards opening the closed co-operating mold sub-assemblies for the purpose of removing the product and separated gutter flash from the apparatus. The forces applied to the gutter flash during such progressive gutter flash separation are tension forces rather than otherwise known conventional cutting or shearing forces.
The blow molding apparatus of the present invention is adapted to be readily installed for functioning in a conventional industrial blow-molding system or machine, and basically is comprised of a base blow-mold sub-assembly having one or more product molds, a co-operating cap blow-mold sub-assembly having a corresponding number of product molds complementary to and in registration with the base blow-mold sub-assembly product molds, a pivotally movable gutter plate that surrounds each base blow-mold sub-assembly product mold, a pivotally movable gutter plate that surrounds each cap blow-mold sub-assembly product mold, at least one bi-directional actuator for pivotally moving said base blow-mold sub-assembly gutter plate, at least one bi-directional actuator for pivotally moving said cap blow-mold sub-assembly gutter plate, and a programmable valve sequence control for properly sequentially actuating the different blow-mold sub-assembly actuators throughout the complete production cycle of the blow-molding machine incorporating the apparatus.